Modal retry diagnostics discard structured command output when appending counters

Additional same-defect evidence from the default Modal recovery path:

attempts=1
signature_matches=0
byte_stable_streams=1
read_tree_signatures=0
lock_path_signatures=0
output_ownership_free=1

This proves the retained event stream remained byte-stable and no ownership token appeared, but the retry command produced a different failure shape. The bounded stdout/stderr needed to classify it is held on CloudWorkerCommandError; appending the aggregate counters currently wraps that object in a plain Error, so the normal worker serializer and failed checkpoint permanently elide the structured phase, exit code, stdout, and stderr.

Minimal generic reproduction:

1. Have the retained retry command exit nonzero with nonempty stdout and stderr.
2. Catch its CloudWorkerCommandError and wrap it with new Error(summary, { cause: error }) to append counters.
3. Pass the wrapper to the worker error serializer.
4. Observe that only the wrapper message survives; the bounded command output is absent.

The smallest correction is to append the counters while rethrowing the original structured command error, preserving the existing fail-closed retry predicates and output bounds.

Start at the default Modal recovery path and trace CloudWorkerCommandError into the worker error serializer, focusing on where aggregate counters are appended. Reproduce a nonzero retry with stdout and stderr, then verify that the serialized error and failed checkpoint retain the structured phase, exit code, and bounded output while retry predicates remain unchanged.